1. Field of the Invention
The present invention relates to a time indicator for indicating the passage of a relative amount of time, and in particular, to a time indicator for indicating the passage of a relatively long amount of time which indicator shows such passage of time by a rapid color change or color switch to clearly show the end of the time interval.
2. Description of the Prior Art
Simple film and paper time indicators are currently being manufactured employing two technologies, one is an opaque film technology which employs dyes diffusing through an opaque film, and the second is a clear film technology which employs a dot pattern of permanent pigment dyes and migrating dyes such that as the migrating dye dots enlarge in size, they develop out a visible image.
Both of these technologies are covered in U.S. Pat. Nos. 4,903,254 dated Feb. 20, 1990, and U.S. Pat. No. 5,058,088 dated Oct. 15, 1991 to David J. Haas, the entire disclosures of which are incorporated herein by reference. These indicators are useful for indicating the passage of relatively short time intervals such as days or weeks. They are not useful for longer time intervals such as months or years because the color change occurs by dye diffusion which begins the instant the activator is applied over the printed dyes. Even though the dye may migrate very slow, these technologies present a problem for the observer in identifying exactly when the image or color change indicates the time interval has occurred.
The prior work in this area has yet to solve the problem of accurately (instantaneously) indicating the passage of a relatively long time interval. Previous efforts are as follows:
U.S. Pat. No. 3,018,611 to Biritz describes a time indicator device which may be used for frozen foods, parking times, construction periods, etc. The device comprises a backing which is attachable to the outer surface of, for example, a package of frozen food. Superimposed on the backing is a strip of filter paper having a chemical reagent laminated thereto. The chemical reagent is an oxygen reactive material. The strip is hermetically sealed by a covering of transparent, impervious pressure sensitive cellophane which allows visual inspection of the oxygen reactive layer. A pin-hole size opening is provided in the covering to allow for ingress of air within the interior of the container. This opening is sealed by a removable tape. When the tape is removed the oxygen reactive material reacts to change color by permitting air to enter and diffuse into the container to make contact with the material. The pin-hole opening is provided at one end of the container and as time proceeds, the color proceeds toward the other unexposed end of the container.
U.S. Pat. No. 3,520,124 to Myers, describes a parked car time indicator which includes a first sheet having a first reactant and a second sheet having a second reactant, and a release sheet, which is peeled away to permit contact of the first sheet with the second sheet to start a reaction over a selective time interval terminating with a color change of the reactants.
U.S. Pat. No. 3,480,402 to Jackson, describes a time indicator formed of an absorbent carrier having absorbed thereon at least one chemical compound which changes color upon exposure to oxygen. The carrier and chemical compound absorbed thereon are protected from ambient oxygen by a non-perforated barrier layer which is transparent and through which atmospheric oxygen can controllably diffuse over a preselected period of time. Thus, when the chemical compound changes color, the preselected period of time is indicated. The graduated time indicator may be produced by utilizing more than one chemical or a layer covering the various pieces of absorbent material of different thickness. For each piece of absorbent material, the chemical absorbed on the piece of absorbent material would change color at different times, e.g., the chemical on one piece would change color after, say, one week, and the chemical absorbed on another piece would change color after ten days, and the chemical on a further piece of absorbent material would change color after fourteen days. Thus, a graduated time indicator is described.
U.S. Pat. Nos. 3,954,011 and 3,962,920 to Manske, describes a time indicating device suitable for visibly measuring parameters such as time, temperature and time-temperature relationships. The device includes a porous fluid-carrying pad, a wick material for said fluid and an indicator means whereby the progress of fluid along the wick material can be visibly indicated and used to measure the passage of time, the exposure to a given minimum temperature or time-temperature relationship.
U.S. Pat. No. 4,028,876 to Delatorre describes an apparatus for visually indicating elapsed time by a color change which comprises a transparent container having a rupturable capsule therein and in which a first composition is contained. A transparent matrix surrounds the second composition which is also in the container. The device may be secured to a surface by means of a mechanical fastener or an adhesive layer.
U.S. Pat. No. 4,212,153 to Kydonieus, et al describes a laminated indicator which changes in a visually perceptible mode with the passage of time. The indicator comprises at least two layers whereby the molecular migration of an agent in an interior layer to the outermost surface of the exterior layer causes a change which is visually perceptible. This reference also describes the use of a step-wedge test color panel placed next to the indicator which is used to compare the developed color or shade. The step-wedge can be provided with indicia corresponding to the time period required to develop the color at each step of the wedge.
Attention is also drawn to U.S. Pat. No. 4,903,254, which is an improvement of the aforementioned Kydonieus et al. patent. It provides a time indicator badge which provides a clear indication of the expiration of time.
U.S. Pat. No. 4,229,813 to Lilly, et al describes a time indicator which utilizes a silicon oil which is slowly absorbed onto and moves up a porous strip at a rate which is a function of time. One side of the strip is printed with an oil soluble ink, while the other side is unprinted. The printed side of the strip is laminated with polyethylene film to an unprinted strip. As the silicon oil moves up the strip, the oil contacts the ink causing a dye in the ink to migrate from the printed side to the unprinted side, thus providing a measurable color front moving up the strip.
U.S. Pat. No. 4,382,700 to Youngren describes an indicator which contains a mineral jelly which is in contact with a wick, such that the mineral jelly diffuses into the paper in accordance with the changes in ambient temperature over a period of time.
U.S. Pat. No. 4,408,557 to Bradley, et al describes a timer comprising an absorptive layer disposed on a base layer which accepts a carrier mixture at a predetermined rate. A barrier means is disposed between the carrier mixture and the absorptive layer, and the removal of the barrier activates the timer.
U.S. Pat. No. 4,629,330 to Nichols describes a color change indicator which includes a liquid having a predetermined index of refraction and a rate of evaporation, a reservoir for holding liquid, and an opacifying layer of microporous material. The opacifying layer has an index of refraction approximately the same as that of a liquid and overlies the reservoir. The opacifying layer has an open cell network of pores for absorbing liquid from the reservoir and is in a first radiation scattering condition when the liquid occupies the opacifying layer, and in a second scattering condition when the liquid is depleted from the opacifying layer.
U.S. Pat. No. 4,643,122 to Seybold describes a diffusion controlled security tag comprising a carrier containing a solution of a compound which changes color upon diffusion or evaporation of the solvent. The carrier is enveloped in a barrier film which controls the rate of diffusion/evaporation of the solvent from the carrier, such that a change in color of the carrier indicates undesirable storage or product tampering.
U.S. Pat. No. 5,107,470 to Pedicano, et al. discloses an indicator wherein a migrating ink bleeds through an opaque layer where it can be seen. The Pedicano device has a base portion and an indicator portion. The base portion includes a clear impermeable base coated onto a non-curing coating having a release sheet. The clear impermeable base carries printed ink, a portion of which contains a migrating agent. The indicator layer includes a clear impermeable top layer, a non-curing indicator layer coating and an indicator release sheet. The non-curing indicator layer coating, upon activation of the indicator, is exposed to and put into adhering contact with base layer to contact the printed ink. Indicator layer is preferably an opaque plasticizer-vinyl-titanium dioxide mixture. This opaque layer provides a background for message display and obscures the non-migrating camouflage component of the printed ink.
One of the problems associated with all of the foregoing devices is that they are difficult to adjust for a selected period of time. Adjustment often involves experimentation with many types of inks, solvents, wicks, etc. to prepare a device which can operate under the conditions expected. Additionally, very few of these devices can indicate the relative length of time that has elapsed since the device was activated, i.e., it is difficult to determine what fraction of the selected period of time has elapsed. Further, none of these devices are suitable for measuring a relative long time period. Most of the prior art devices gradually change color over a relatively short period of time and involve, at best, a guess on how much time has elapsed. When this is combined with the possible variations in temperature, humidity, etc. that may exist in the environment of the time indicator, the viewer has very little confidence that he is close to the expiration time of the device.
None of these references teach or suggest the applicant's claimed invention. Applicant, with its invention has met a need that exists for an indicator which is inexpensive and can clearly, relatively accurately and quickly indicate the passage of relatively long time intervals.